1. Field of the Invention
The present invention relates to a burst-mode optical receiver, and more particularly to a burst-mode optical receiver capable of determining an input signal and generating on its own a reset signal for the initialization between packets intervals.
2. Description of the Related Art
The next generation of communication services require FTTH (Fiber-To-The Home) communications systems, which proves an optical fiber connected to subscribers' homes directly for enabling higher transmissions of data. It is costly, however, to replace the existing copper-based subscriber lines with this type of optical subscriber lines. To overcome this problem, PONs (Passive Optical Networks) are presently considered to provide low-cost optical subscriber lines for a faster data transmission.
FIG. 1 illustrates a passive optical network system, which consists of an optical line termination (OLT) located in a central office, a 1×N passive optical splitter, and a plurality of optical network units (ONUs) located in the subscriber's premise.
As shown, each node transmits data or packets to another node using a predetermined time slot. The multi-access network is different from a point-to-point link in that it generates burst-mode data of varying sizes and phases due to the optical loss on different transmission paths. Also, the sizes of data packets received vary due to the difference in the transmission path lengths from and to the subscribers' premises. Note that it is possible for many subscribers to communicate via a single fiber optic strand using a time-division multiplexing scheme. Therefore, a current trend is to use a burst-mode optical receiver, which receives data of various sizes and phases, then restores the data back to the same size and phase for all received packets.
The burst-mode optical receiver excludes a DC block capacitor that has been used in AC coupling of a general receiver, thereby preventing a burst data loss during charge or discharge time of the capacitor. In addition, the burst-mode optical receiver extracts a detection threshold as a reference signal for data determination purposes from each burst packet being received. Thus, the burst-mode optical receiver must have a function of restoring data by amplifying the data based on the extracted detection threshold symmetrically.
FIG. 2 is a schematic view showing the construction of a conventional burst-mode optical receiver. The burst-mode optical receiver comprises an optical detector 1, a pre-amplifier 2, an automatic threshold controller (ATC) 3, and a limited amplifier 4.
The optical detector 1 converts an input optical signal to a current signal. The pre-amplifier 2 converts the current signal detected at the optical detector 1 to a voltage signal. A transimpedance, which refers to the ratio of an input current to an output voltage, is determined by a feedback resistor (Rf) that is connected to the input and output terminals of a transimpedance amplifier (TIA). The TIA 2 is a DC-coupled to be used in a burst-mode optical receiver. A signal in the TIA 2 is amplified and then divided into two segments. One segment of the signal is inputted to an ATC 3 to extract a detection threshold of the received packet, while the other segment is DC-coupled and inputted to a limited amplifier 4. The detection threshold that automatically changes according to the packet size is inputted to the Vref of the limited amplifier 4. The limited amplifier 4 amplifies signals of varying levels received therein in order to restore the signals to exhibit a uniform amplitude.
However, in the burst-mode optical receiver described above, a reset signal for the initialization of packet intervals is performed using an external circuit, which complicates the circuit of the optical receiver and increases the component size of the receiver. Therefore, there is a need for an improved optical receiver that is simple and reliable implementation.